Controlling an injection of fuel into a combustion chamber of a cylinder of an internal combustion engine is a complex task. For example, a point of injection and an injection quantity of the fuel to be injected must be precisely determined. These two parameters may, however, change during an operation of the internal combustion engine, for example as a function of an operating point, and/or over a service life of the internal combustion engine.
A method is described in German Patent No. DE 10 2014 215 618 A1 in which a fuel injection quantity, which is withdrawn from a high-pressure accumulator of an injection system designed as a common-rail system and injected into one or multiple combustion chambers of the cylinders of an internal combustion engine, assigned in each case, is determined during the operation of the internal combustion engine. For this purpose, a fuel pressure in the high-pressure accumulator is detected as a function of an angle and transferred into a frequency-transformed pressure spectrum of the fuel pressure. The injection quantity is ascertained from an amplitude of the frequency-transformed pressure spectrum at the point in time of the ignition frequency of the internal combustion engine. The ascertained injection quantity corresponds in this case to the injection quantities averaged over all cylinders of the internal combustion engine.
It is desirable to operate an internal combustion engine in such a way that the injection of the internal combustion engine may be implemented particularly precisely and easily.